Vinyl acetate/ethylene (VAE) emulsions have been widely produced for use as adhesives, coatings, paints, and other applications. One of the recent trends in vinyl acetate/ethylene polymer emulsion technology is to increase the solids content to a level above about 65% by weight, preferably to a level of at least from 65 to 75% by weight. Customary commercial vinyl acetate/ethylene emulsions typically have a solids content of from 54-56%. The former emulsions are referred to as "high solids" emulsions and offer many advantages in addition to the fact there is more product per unit weight. Representative patents for producing batch high solids vinyl acetate/ethylene emulsions are as follows:
U.S. Pat. No. 4,921,898 discloses a process for producing vinyl acetate/ethylene copolymer emulsions having from about 65-70% solids which emulsion is prepared in the presence of a stabilizing system consisting essentially of 2-4 wt % polyvinyl alcohol having a degree of polymerization of from 100 to 600 and from about 2-4 wt % of a surfactant such as condensates of ethylene oxide and a hydrophobic base and alkylphenoxy poly(ethyleneoxy) ethanol, the surfactants being sold under the trademarks Pluronic and Igepal, respectively.
U.S. Pat. No. 5,124,394 discloses a process for producing high solids vinyl acetate/ethylene copolymers utilizing a stabilizing system consisting essentially of poly(ethyloxazoline). Optionally, a low molecular weight polyvinyl alcohol having a molar percent hydrolysis of from 75-99% and an average degree of polymerization from 100 to 600 is included as a component of the stabilizing system. Also, one can incorporate small levels of alkylphenoxy poly(ethyleneoxy) ethanols and ethylene oxides of hydrophobic bases.
U.S. Pat. No. 5,070,134 discloses a process for producing high solids vinyl acetate/ethylene emulsions having a solids content of from 65-70% by weight utilizing an emulsifying dispersant containing from 1 to 1.9 parts by weight partially saponified polyvinyl alcohol having an average polymerization degree of from 300 to 1,000 and from 1 to 3 parts by weight of a polyoxyethylene nonionic surface active agent having an HLB of from 16.5 to 17.5 per hundred parts by weight of vinyl acetate units.
U.S. Pat. No. 5,629,370 discloses a process for producing vinyl acetate/ethylene copolymers having a solids content of at least 65% by weight utilizing from 0.8 to 2 percent by weight of a fully or partially hydrolyzed polyvinyl alcohol in a mixture of nonionic, ethoxylated alkylphenol surfactants having an HLB of from 16.0 to 16.5.
Vinyl acetate/ethylene emulsions have also been prepared by continuous processes, but largely the continuous processes have been used for the production of polyvinyl acetate homopolymers and vinyl acetate/ethylene emulsions at conventional, 54-56% solid levels. Representative patents are as follows:
U.S. Pat. No. 4,164,489 discloses a continuous process for producing vinyl acetate/ethylene copolymer emulsions for use in adhesive applications. The solids content of the emulsions range from about 40-65% with a general range of between 50 and 60% solids. The stabilizer used for the polymerization consisted of polyvinyl alcohol typically having a molar hydrolysis of 87-89% and a viscosity of 21-25 cps at 4% solids at .about.20.degree. C. Initial polymerization of vinyl acetate and ethylene is carried out in the presence of a seed latex and then removing the latex from the initial polymerization vessel at a vinyl acetate monomer content of from 5-20% by weight.
U.S. Pat. No. 2,587,562 discloses a process for continuous polymerization of vinyl acetate utilizing a stabilizing system of hydroxyethyl cellulose and sodium sulfonate.
U.S. Pat. No. 3,551,396 discloses a process for producing a variety of vinyl polymers by polymerizing such vinyl monomers in a "loop" reactor. The stabilizing system employed in the loop reactor is a polyoxyethylene-polyoxypropylene copolymer.
U.S. Pat. No. 4,035,329 discloses a process for the continuous production of an ethylene/vinyl acetate copolymer in the presence of a redox catalyst system in which the oxidizing component of the redox catalyst system is in molar excess of from 3 to 10 times the presence of the reducing agent, and the monomers are added at a rate such that the unreacted vinyl monomer concentration does not exceed 15% by weight.
U.S. Pat. No. 5,442,006 discloses a process for producing vinyl acetate and acrylic dispersions having wide particle size range. A wide variety of surface active substances containing polymer are suited for stabilizing the emulsion, and these include polyvinyl alcohol, cellulose derivatives, and vinyl pyrrolidone containing copolymers as well as other nonionic, cationic, and anionic emulsifiers.